DE102010006204A1 - Photovoltaic module manufacturing method, involves providing substrate with layer sequence comprising photoactive layer stack, and applying back contact on one of regions of n-doped layer, where one of regions has homogeneous thickness - Google Patents

Abstract

The method involves providing a substrate (1a) of a photovoltaic cell (100) with a layer sequence comprising a photoactive layer stack (3b), where the stack comprises a p-doped layer (31b), an intrinsic layer (32b) and an n-doped layer (33b). The n-doped layer is provided with two regions (5a, 5b) with different oxygen concentration. A back contact (4) is applied on one of the regions of the n-doped layer, where one of the regions has a homogeneous thickness. Controlled ventilation is produced in an intermediate memory.

Description

The invention relates to a method for producing a plurality of photovoltaic modules, each comprising a plurality of photovoltaic cells.

Photovoltaic modules have a plurality of photovoltaic cells, which may be formed as so-called tandem junction photovoltaic cells, wherein the photovoltaic cells each have an optically and electrically coupled in series substantially amorphous silicon comprehensive layer stack and a substantially microcrystalline silicon comprehensive layer stack. For this purpose, layers of the individual layer stacks are deposited on a substrate by means of, for example, a CVD method (CVD: Chemical Vapor Deposition). Subsequently, a rear-side contact is formed on the upper layer stack by means of a coating method. The layer stacks can then be encapsulated by, for example, another substrate.

Before the rear contact is applied to the layer stack, owing to unsaturated silicon layers, the layer stack can accumulate oxygen on the surface of the uppermost layer of the layer stacks and diffuse into the layers of the layer stacks. In particular, an upper region can thus be formed in the layer stack of silicon, which is chemically reformed by chemically bonding oxygen. As a result, for example, a silicon oxide layer can form in the upper region of the layer stack.

When producing a plurality of photovoltaic modules, the regions of the layer stacks of the individual photovoltaic modules which comprise bound oxygen usually have a different thickness due to an uncontrolled accumulation of the oxygen relative to one another. Accordingly, the different photovoltaic modules have regions of bound oxygen which have an inhomogeneous or non-uniform thickness relative to each other.

An inhomogeneous thickness of the layer regions of the modules is understood in particular to mean differences in the statistical distribution of the thickness of these layer regions from module to module. As a result, however, the electrical properties of such modules can deteriorate, which can adversely affect the stability of the efficiency of the photovoltaic modules. In particular, a plurality of modules with an inhomogeneous thickness have different powers from each other.

It is an object of the present application to provide an improved manufacturing method for a plurality of photovoltaic modules, which is characterized in particular by producing a homogeneous thickness of the regions of the individual photovoltaic modules to each other, the oxygen bound, whereby an increased stability of the module efficiency can be achieved.

This object is achieved inter alia by a production method of a plurality of photovoltaic modules having the features of claim 1. Advantageous embodiments and preferred developments of the manufacturing method are the subject of the dependent claims.

• – jeweils Bereitstellen eines Substrats mit einer darauf aufgebrachten Schichtenfolge umfassend zumindest einen photoaktiven Schichtstapel, der zumindest eine p-dotierte Schicht, eine intrinsische Schicht und eine n-dotierte Schicht aufweist, wobei die n-dotierte Schicht zumindest einen ersten Bereich und einen zweiten Bereich umfasst, die eine unterschiedliche Sauerstoffkonzentration aufweisen, und
• – jeweils Aufbringen eines Rückseitenkontakts auf den zweiten Bereich der n-dotierten Schicht, sodass jeweils ein Photovoltaikmodul hergestellt wird, wobei
• – die zweiten Bereiche der einzelnen Photovoltaikmodule eine zueinander homogene Dicke aufweisen.

In an embodiment, the method for producing a plurality of photovoltaic modules, each comprising a plurality of photovoltaic cells, comprises the following method steps:

• - Each providing a substrate having a layer sequence applied thereto comprising at least one photoactive layer stack having at least one p-doped layer, an intrinsic layer and an n-doped layer, wherein the n-doped layer comprises at least a first region and a second region having a different oxygen concentration, and
• - Each applying a back-side contact on the second region of the n-doped layer, so that in each case a photovoltaic module is produced, wherein
• - The second areas of the individual photovoltaic modules have a mutually homogeneous thickness.

In the present method, oxygen is selectively incorporated into the n-doped layer of silicon, so that a silicon oxide layer or a silicon oxide region is preferably produced in the n-doped layer. In particular, the oxygen in the n-doped layer is stored in a controlled manner and chemically bound there, which advantageously counteracts climatic fluctuations in production, such as fluctuations in temperature, humidity and the like, which can disadvantageously lead to a fluctuation in the efficiency of the photovoltaic module can be. In particular, the performance of the modules thus exhibit slight fluctuations or deviations from one another, as a result of which such modules are distinguished by virtually the same performance.

In particular, differences in the thickness of the second region of the n-doped layer between the different modules can thus be avoided, as a result of which the electrical properties at the interface between the back contact and the adjacent n-doped layer of different modules can advantageously be adapted to one another. This way with advantage such produced photovoltaic modules to a homogeneous thickness of the second region of the n-doped layer to each other, whereby in operation an increased stability in the efficiency can be achieved.

In addition, by targeted production of the second region with bound oxygen, an uncontrolled diffusion of oxygen into the individual layers of the layer stack, in particular into the intrinsic layer, can advantageously be avoided.

In the context of the present application, an area with a homogeneous thickness of a module means, in particular, that this area has a substantially equal thickness over the area with respect to a complementary area of a further module, which is manufactured using the same manufacturing method. These include, inter alia, layers which, due to the manufacturing process, have small variations in thickness in certain areas. For example, in the context of the application, areas with thickness deviations of 10% are understood as areas with a substantially uniform thickness.

Preferably, variations in the thickness of the second region between different modules are kept as low as possible. In particular, statistical thickness distributions over the manufacturing process between different modules are preferably kept as low as possible.

In the context of the present application, an intrinsic layer is to be understood as meaning a layer which is substantially undoped. Foreign substances, such as, for example, impurities in the layer, are not regarded as doping in the context of the application.

In one embodiment, the photovoltaic module comprises a further photoactive layer stack which has at least one further p-doped layer, a further intrinsic layer and a further n-doped layer, wherein the further layer stack is arranged on the side of the photoactive layer stack opposite the rear contact.

Preferably, at least one layer of the photoactive layer stack mainly comprises microcrystalline silicon. Particularly preferably, at least one layer of the further photoactive layer stack predominantly comprises amorphous silicon. The n-doped layer of the layer stack preferably comprises predominantly amorphous silicon.

The n-doped layer preferably has diffused oxygen which decreases in quantity in the direction of the intrinsic layer.

In one embodiment, the photovoltaic module comprises a plurality of stacked layers, each comprising at least a p-doped layer, an intrinsic layer and an n-doped layer.

In a further embodiment, the plurality of photovoltaic modules are manufactured in a consecutive manufacturing process. The layers of the individual photovoltaic modules are preferably deposited in each case on successive substrates.

In a further embodiment, the production of the second region comprises a deposition process in a PECVD process (PECVD: plasma-enhanced chemical vapor deposition). By way of example, during the deposition of the n-doped layer of the photoactive layer stack in a silane-H ₂ plasma, the second region, in particular a silicon oxide layer, can be selectively deposited by briefly switching on a CO ₂ gas flow or an N ₂ O gas flow , Preferably, some monolayers of silicon oxide (SiO _x ) are deposited.

The second region preferably has a layer thickness in a range between a few monolayers of silicon oxide to thicknesses including 20 nm. Preferably, the second region has a thickness in a range between 2 nm inclusive and 20 nm inclusive. More preferably, the second region has a thickness in a range between 2 nm and 10 nm inclusive.

In a further embodiment, the production of the second region comprises a deposition process in a PVD (Physical Vapor Deposition) process. By way of example, the production of the silicon oxide layer comprises a sputtering process from a silicon target (Si target) in an oxygen / argon plasma (O / Ar plasma). Preferably, by adjusting the oxygen content of the oxygen / argon plasma, the optical properties, in particular the refractive index of the photovoltaic module, can be adjusted, in particular adapted to a predetermined value. The sputtering process preferably includes a DC sputtering process or an RF sputtering process.

In a further embodiment, the production of the second region comprises a post-treatment of the n-doped layer of the layer stack by an oxygen plasma (O plasma), an oxygen argon plasma (O / Ar plasma), an N ₂ O plasma and / or a CO ₂ plasma. Preferably, the oxygen plasma, the N ₂ O plasma and / or the CO ₂ plasma may be mixed with argon.

In a further embodiment, the photovoltaic module is conditioned in an intermediate store before the second area is produced. In particular, the photovoltaic module is stored in the intermediate store between the deposition of the n-doped layer of the layer stack and before the application of the back contact for several hours.

The buffer preferably has defined climatic conditions. Preferably, the temporary storage over the storage time only slight fluctuations in the climatic conditions. Particularly preferably, the variations in the climatic conditions in the buffer are less than 10%.

Preferably, the temperature in the buffer is set in a range between 10 ° C inclusive and 70 ° C inclusive, more preferably between 20 ° C inclusive and 70 ° C inclusive. Preferably, the humidity in the buffer is set to greater than 30% relative humidity, preferably greater than 50% relative humidity, more preferably greater than 70% relative humidity. Particularly preferably, a controlled ventilation takes place in the buffer.

In another embodiment, a humidifier is created in the buffer, which enriches the air with fine water particles. In particular, an artificial enrichment of the air with water particles takes place here. For example, a water mist or a fine precipitate by means of, for example, a spray device is generated in the buffer so that a droplet-enriched air is formed in the buffer, which is preferably reflected on the module. In this case, the module produced so far is particularly preferably cooled, so that the water accumulates on the surface of the substrate by condensation.

As a result, fluctuations in the efficiency between different photovoltaic modules, which can occur due to climatic fluctuations in production, can advantageously be avoided. In particular, such variations in the thickness of the second region of the n-doped layer of the different modules may arise due to different storage times of the individual modules, which however are advantageously reduced by the targeted incorporation of the oxygen in the second region of the n-doped layer of the individual modules can.

A method of manufacturing a photovoltaic module comprising a plurality of photovoltaic cells preferably comprises a common manufacturing method of the individual photovoltaic cells. The individual photovoltaic cells of the photovoltaic module are preferably produced in a so-called common composite.

In one embodiment of the production method of the photovoltaic module, the layers of the photovoltaic cells are deposited over a large area on a common substrate and then separated into individual photovoltaic cells by means of one or more structuring methods. The structuring method preferably comprises a laser structuring method or a mechanical method.

In another embodiment, the photovoltaic modules are silicon thin film photovoltaic modules. Silicon thin film photovoltaic modules have photoactive layers of a thickness in the range of a few 10 nm to a few micrometers. Silicon thin-film photovoltaic modules represent a balanced and thus cost-effective variant of such photovoltaic modules in terms of their efficiency in the conversion of radiant energy into electrical energy and the production costs.

A photovoltaic module according to an embodiment comprises a plurality of photovoltaic cells electrically coupled in series.

Further advantages, advantageous embodiments and developments of the invention will become apparent from the following in connection with the 1 to 3 described embodiments.

Show it:

1 a schematic representation of a photovoltaic cell according to an embodiment,

2 a schematic plan view of a photovoltaic module according to an embodiment, and

3 a flowchart for a method of manufacturing a photovoltaic module according to an embodiment of the invention.

In the exemplary embodiments and figures, identical or identically acting components may each be provided with the same reference numerals. The illustrated elements and their proportions among each other are basically not to be considered as true to scale, but rather individual elements, such as layers, components, components and areas, for exaggerated representability and / or for better understanding, can be shown exaggeratedly thick or large.

In 1 is an embodiment of a photovoltaic cell 100 shown, which is preferably part of a photovoltaic module. In particular, a photovoltaic module is made up of a series of photovoltaic cells which are electrically connected to one another 100 together, as for example in 1 is shown.

The photovoltaic cell 100 has a substrate 1a on which a front side contact 2 is applied. On the front side contact 2 are two photoactive layer stacks 3a . 3b arranged, each in the finished photovoltaic cell 100 are suitable to light that through the substrate 1a and the front side contact 2 falls to absorb to form pairs of electron holes and thereby generate an electric current.

The substrate 1a is set up, the layer stacks 3a . 3b to wear. The substrate 1a is especially transparent for radiation in the visible spectrum and in the infrared range and has a high transparency in a wavelength range of 400 nm to 1100 nm. The substrate 1a includes, for example, glass, in particular low-iron flat glass, silicate glass or rolled glass.

The front side contact 2 comprises a transparent conductive oxide (TCO), for example zinc oxide or tin oxide. The substrate 1a and the front side contact 2 together have a transparency of greater than 80% in a wavelength range of 400 nm to 1100 nm.

The first photoactive layer stack 3a has a layer sequence formed from a p-doped layer 31a , an intrinsic, undoped layer 32a and an n-doped layer 33a on. Preferably, at least one layer of the first photoactive layer stack has 3a predominantly amorphous silicon. At least the intrinsic layer is particularly preferred 32a predominantly amorphous silicon. The first layer stack 3a is preferably configured to at least partially convert the energy of the incident during operation radiation into electrical energy (internal photoelectric effect).

The second photoactive layer stack 3b has a layer sequence formed from a p-doped layer 31b , an intrinsic, undoped layer 32b and an n-doped layer 33b on. Preferably, at least one layer of the second photoactive layer stack has 3b predominantly microcrystalline silicon. At least the intrinsic layer is particularly preferred 32b predominantly microcrystalline silicon. The second photoactive layer stack 3b is arranged to convert the energy of the incident during operation radiation at least partially into electrical energy.

Due to the different absorption spectra of amorphous and microcrystalline silicon, a broad absorption spectrum and thus a high quantum efficiency can be achieved in such a so-called tandem cell.

For example, boron is used as the p-type dopant, while, for example, phosphorus is used as the n-type dopant.

Preferably, the first photoactive layer stack converts 3a Radiation of wavelength up to about 700 nm more effectively into electrical energy and the second photoactive layer stack 3b Radiation with a longer wavelength of up to 1100 nm more effective.

On the second layer stack 3b is a backside contact 4 arranged, for example, of a plurality of layers 4a . 4b composed. For example, the backside contact comprises a TCO layer 4a , for example comprising ITO, SNO ₂ or ZNO. The layer 4b is preferably a metallic layer, preferably comprising Al, Ag, Ti, TiO _x , and / or a metal alloy. Preferably, the layer is 4b highly reflective designed.

Optionally, on the backside contact 4 a nickel vanadium layer may be arranged which preferably protects the metallic layer from corrosion (not shown). On the backside contact 4 or optionally on the nickel vanadium layer can be arranged for external electrical contacting a soldering tape, for example a copper tape (not shown).

The front side electrode 2 and the backside electrode 4 serve for electrical contacting of the two series-connected photoactive layer stacks 3a . 3b and are set up during operation electric current or electrical voltage from the two photoactive layer stacks 3a . 3b dissipate.

The photovoltaic cell 100 is preferably designed as a thin-film photovoltaic cell.

Around the photoactive layers 3a . 3b Can protect against damage and environmental influences, on the back contact 4 preferably one flat material 1b , For example, a further glass pane, be applied (not shown).

The n-doped layer 33b of the second layer stack 3b has a first area 5a and a second area 5b on the back contact 4 is facing. The n-doped layer 5 preferably has silicon. In the second area 5b Preferably, oxygen is chemically bound. The second area 5b thus preferably has silicon oxide.

Preferably, the second area 5b a uniform thickness in a range between 2 nm inclusive and 20 nm inclusive. More preferably, the thickness is in the range of a few monolayers up to and including 10 nm.

Preferably, the second area 5b The n-doped layer has been produced specifically in the manufacturing process. Such targeted production is particularly in connection with 3 explained in more detail.

In 2 an embodiment of a photovoltaic module is shown that a plurality of photovoltaic cells 100 . 100a having. In particular, the photovoltaic cells are coupled mechanically and electrically in series.

Preferably, the photovoltaic module 200 designed as a thin film module. Thin film modules have photoactive layers of a thickness in the range of a few 10 nm to a few micrometers. Usually, the photoactive layers are applied over a large area to a substrate, for example a glass pane, together with contact and optionally reflection layers. With the aid of one or more structuring steps, a plurality of individual strip-shaped photovoltaic cells 100 . 100a formed, which are preferably connected in series. The width of the strip-shaped photovoltaic cells is in the range of about 7 mm to 25 mm.

On the outer photovoltaic cells 100a usually pantographs are applied, via which the thin-film module is connected and the generated electrical power can be dissipated. The outer photovoltaic cells 100a thus do not serve to convert light into electrical energy, but for external electrical contact. For this purpose, for example, galvanized copper strips as a current collector on the outer photovoltaic cells 100a soldered.

To reinforce the module, a circumferential frame, for example made of aluminum can be used. In the case of photovoltaic modules without such a frame, so-called frameless thin-film modules, the module can be arranged on a carrier element or a plurality of carrier elements to stabilize and support the carrying capacity. Before the application of the carrier element, the semiconductor layers of the photovoltaic module, in which, for example, the semiconductor layers are arranged between two glass substrates, are completely deposited. The module 200 can then be coupled to a ground.

The photovoltaic cells 100 one like in 2 illustrated module 200 For example, a layer structure as in the embodiment of 1 shown have.

In 3 FIG. 3 is a flowchart showing process steps of a manufacturing method according to an embodiment. FIG. The flowchart shows in particular a production method for producing a photovoltaic module.

In step 301 a plurality of layers is applied over a whole area on a substrate, the layers in particular forming photoactive layer stacks. In particular, a TCO layer, a p-doped layer, an intrinsic layer, an n-doped layer, a further p-doped layer, an intrinsic layer and a further n-doped layer are applied over the entire surface of a substrate.

In the process step 302 The substrate is conditioned with the layers applied thereto in a buffer. In particular, the buffer has a temperature in a range between 20 ° C and 70 ° C inclusive. Preferably, temperature fluctuations in the buffer preferably occur hardly or not. Particularly preferably, the temperature fluctuations in the buffer are less than 10%.

The humidity in the buffer is preferably set to greater than 30% relative humidity, preferably greater than 50% relative humidity, more preferably greater than 70% relative humidity. Fluctuations in the humidity preferably occur hardly or not. Fluctuations in the humidity in the buffer are particularly preferably less than 10%.

Preferably, a controlled ventilation is generated in the buffer. Particularly preferably, a humidifier is generated in the buffer, which enriches the air in the buffer with fine water particles.

In the cache with defined climatic conditions, the module for several Hours are stored before it is processed further. In particular, the influence of climatic conditions in the production of the modules can thus be reduced, so that, with advantage, fluctuations in the module efficiency can be reduced.

step 303 includes a laser contacting step. In particular, the individual layers of the photovoltaic cells for integrated series connection of the individual photovoltaic cells are each structured according to their deposition method by means of at least one structuring method, for example by means of a laser structuring method. Such structuring methods for the integrated series connection of individual photovoltaic cells are known to the person skilled in the art and are therefore not explained in greater detail here.

In the process step 304 the n-doped layer of the second layer stack is treated such that form therein a first region and a second region. In particular, oxygen is incorporated and chemically bound in the second region. The second region thus preferably comprises silicon oxide. Preferably, after the process step 304 the first region and the second region of the n-doped layer have a different oxygen concentration.

The second region is preferably produced by means of a PECVD process. For example, in the deposition of the n-doped layer of the second layer stack in a silane / H ₂ plasma by the temporary connection of a CO ₂ gas flow, an N ₂ O gas or an oxygen gas targeted the second area can be produced, the for example, a few monolayers thick.

Alternatively, the second region may be made in a PVD process. For example, the second region is formed by sputtering from a silicon target (Si target) in a variable oxygen content oxygen argon plasma (O / Ar plasma).

Alternatively, the second region can be produced by means of a post-treatment of the n-doped layer by an oxygen or an oxygen argon plasma (O / Ar plasma).

By means of such a production method, a plurality of photovoltaic modules can advantageously be produced in succession, which in particular are characterized by a mutually homogeneous thickness of the second regions. As a result, in particular photovoltaic modules can be manufactured, which are characterized by a stability in the module efficiency.

For this purpose, the individual photovoltaic modules by means of the described method steps 301 to 304 manufactured sequentially. The individual photovoltaic modules are therefore subjected to the same manufacturing process one after the other.

Subsequently, in the steps 305a and 305b each applied a backside contact on the second region of the n-doped layer. The backside contact may preferably be composed of a plurality of layers.

For example, in step 305a applied to the n-doped layer, a zinc oxide layer by means of a PVD coating process.

On the zinc oxide layer can then in step 305b a metallic layer, for example a silver-containing layer, can be applied by means of a PVD process.

The individual PVD method steps preferably each include a sputtering process.

In step 306 Optionally, a protective layer, for example made of nickel vanadium, and / or contact strips comprising copper, for example, can be applied to the back side contact.

Subsequently, optional in step 307 in each case a protective layer, for example of polyvinyl butyral (PVB) or a thermoplastic and / or a cover glass are laminated so that the modules are encapsulated in order to protect the photoactive layers from damage and environmental influences.

The individual layers of the photovoltaic module can each be patterned directly after their deposition process into photovoltaic cells, for example by means of one or more patterning steps, whereby a plurality of individual strip-shaped photovoltaic cells are formed, which are electrically connected in series.

The invention is not limited by the description based on the embodiments of these. Rather, the invention encompasses any novel feature as well as any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary embodiments.

LIST OF REFERENCE NUMBERS

1a

substratum

1b

encapsulation

2

Front contact

3a

first photoactive layer stack

3b

second photoactive layer stack

4

Back contact

4a

TCO layer

4b

mirror layer

5a

first region of the n-doped layer

5b

second region of the n-doped layer

31a, b

p-doped layer

32a, b

intrinsic layer

33a, b

n-doped layer

100, 100a

photovoltaic cell

200

photovoltaic module

301-307

Process steps in the production of a photovoltaic module

Claims (17)

Method for producing a plurality of photovoltaic modules ( 200 ), each having a plurality of photovoltaic cells ( 100 ), wherein the production of a photovoltaic module ( 200 ) comprises the following method steps: providing a substrate ( 1a ) with a layer sequence applied thereto comprising at least one photoactive layer stack ( 3b ) comprising at least one p-doped layer ( 31b ), an intrinsic layer ( 32b ) and an n-doped layer ( 33b ), wherein the n-doped layer ( 33b ) at least a first area ( 5a ) and a second area ( 5b ), which have a different oxygen concentration, and - application of a backside contact ( 4 ) to the second area ( 5b ) of the n-doped layer ( 33b ), where - the second areas ( 5b ) of the individual photovoltaic modules have a mutually homogeneous thickness. The method of claim 1, wherein the plurality of photovoltaic modules ( 200 ) are manufactured in a sequential manufacturing process. Method according to one of the preceding claims, wherein the n-doped layer ( 33b ) each comprise silicon and at least the second region ( 5b ) each comprises silicon oxide. Method according to one of the preceding claims, wherein the second area ( 5b ) each having a thickness in the range of a few monolayers of silicon oxide up to and including 20 nm. Method according to one of the preceding claims, wherein the production of the second area ( 5b ) each comprise a deposition process in a PECVD process. Method according to one of the preceding claims 1 to 5, wherein the production of the second area ( 5b ) each comprises a deposition process in a PVD process. Method according to claim 6, wherein the production of the second area ( 5b ) each comprise a sputtering process from a silicon target in an oxygen / argon plasma. The method of claim 7, wherein adjusting the oxygen content of the oxygen / argon plasma, the optical properties of the photovoltaic module can be adjusted. Method according to one of the preceding claims 1 to 5, wherein the production of the second area ( 5b ) each a post-treatment of the n-doped layer ( 33b ) by an oxygen plasma, an oxygen / argon plasma, an N ₂ O plasma and / or a CO ₂ plasma. Method according to one of the preceding claims, wherein prior to the production of the second area ( 5b ) the photovoltaic module ( 200 ) is conditioned in each case in a buffer. A method according to claim 10, wherein in the buffer the temperature is set in a range between 10 ° C inclusive and 70 ° C inclusive. Method according to one of the preceding claims 10 or 11, wherein the humidity in the buffer is set to greater than 30% relative humidity. Method according to one of the preceding claims 10 to 12, wherein in the buffer a controlled ventilation is generated. Method according to one of the preceding claims 10 to 13, wherein variations in the climatic conditions are less than 10% in the buffer. Method according to one of the preceding claims 10 to 14, wherein in the buffer a humidifier is generated, which enriches the air with fine water particles. Method according to one of the preceding claims, wherein the photovoltaic modules are each silicon thin-film photovoltaic modules. Method according to one of the preceding claims, wherein the photovoltaic modules each have a further photoactive layer stack ( 3a ) comprising at least one further p-doped layer ( 31a ), another intrinsic layer ( 32a ) and another n-doped layer ( 33a ), wherein the further layer stack ( 3a ) on the backside contact ( 4 ) opposite side of the photoactive layer stack ( 3b ) is arranged.

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